The present invention relates to repeaters used in computer networks. Specifically, the invention relates to integrating a plurality of twisted pair Medium Attachment Units ("MAU") with a repeater in monolithic silicon and providing port expansion capability.
Businesses use computer networks to improve productivity. Many different network types were developed to aid this productivity improvement. One such network type is a Carrier Sense, Multiple Access--Collision Detection ("CSMA/CD") network. IEEE 802.3 Standard, hereby expressly incorporated by reference for all purposes, specifies working characteristics for a CSMA/CD network. A commercial system known as ETHERNET.RTM., a registered trademark of Xerox Corporation, is an example of such a system.
CSMA/CD networks provide a plurality of nodes which have a controller to interface to the network. The nodes may be any type of data terminal equipment ("DTE") for transferring data to another DTE. The controller conditions incoming and outgoing data and control signals according to the particular network protocol. It is possible to use one or more medium types to carry the communication signals. This medium is often coaxial cable because of the cable's well known and predictable parameters. The different protocols available each requires structured data and control information. The controller prepares data and control information according to the specific protocol used. The data and control information become data and control signals. These signals are independent of the actual medium used. Translating these medium independent signals into signal types specific to the particular medium is the function of the MAU. An attachment unit interface ("AUI") couples the controller and the MAU. The IEEE 802.3 Standard defines the protocol between the AUI and the MAU as well as the AUI characteristics.
An obstacle to greater use of computer networks is installation costs. Retrofitting a building with necessary wiring to use a network can require relatively large costs for installing the network. Development of a network protocol which operates over preexisting telephone lines reduces the installation cost by removing some of the wiring expense. The preexisting telephone wiring typically uses twisted pair cable. Problems of the twisted pair cable directly relate to its lack of shielding making it vulnerable to noise. Using the twisted pair cable as a network medium complicates network installation because ambient noise interferes with network operation. There are also limitations on electromagnetic radiation emissions from an operating network. These limitations become more difficult to meet due to the lack of shielding for the wiring. Also, line characteristics of preinstalled wiring networks are unpredictable making impedance matching difficult, further complicating specifications for signal drivers and receivers.
A group of manufacturers jointly developed a 10BASE-T draft standard, hereby expressly incorporated by reference for all purposes. The draft standard enables network use of twisted pair wiring. The 10BASE-T draft standard outlines devices and device characteristics to carry out a CSMA/CD protocol through a twisted pair medium. This draft standard defines the MAU and its operation. Many networks realizing the IEEE 802.3 Standard use a medium (such as coaxial cable) in a bus-type topology from which multiple nodes depend. The 10BASE-T draft standard, however, requires a star-type topology (when three or more nodes are present) due to the twisted-pair medium. This star-type topology has a repeater at a hub of the star. The repeater functions to receive data from one of a plurality of ports. After extracting an embedded clock signal from the data, the repeater processes the data with its own internal clock. The repeater then broadcasts to all of its ports the newly timed and amplitude-corrected data. A repeater may, if it includes an AUI port or coaxial MAU, connect to a multi-drop bus at one of its ports. Thus, many nodes may connect to the single repeater port.
To meet timing requirements outlined in the IEEE 802.3 Standard, a network has a maximum of four repeaters in any series from one node to any other node. Therefore, the number of available ports on a particular repeater significantly impacts the number of possible users of a network structured using star-topology. Limited port availability on repeaters prevents network growth and limits use of discrete repeater components. Especially considering that star-topology results in one node per repeater port.
Conventional repeaters have virtually unlimited expansion capacity. A network administrator adds ports as necessary and the network increases virtually without bound. Conventional repeaters separate the relay function, the actual repeater, from the medium attachment function of the MAU. That is, the repeater function remains constant and ports are simply added.
To provide this expansion capability, costs of repeaters can be significant. Reduction of repeater costs results from providing monolithic devices incorporating the repeater functions. Further cost reduction is possible by integrating the repeater functions and the MAU functions. However, integration of the MAU and the repeater into a single monolithic device prevents simple addition of ports as was done in the past. Each single chip will have a limited number of ports available due to drive current limitations. As the reader will appreciate, this number will be relatively small. Combining this limited port availability with the further limit of no more than four repeaters in series, restricts the size of networks offered by monolithic devices. For small networks this size limitation is acceptable. Such integrated repeater and MAU units would be unacceptable for larger networks or for instances of anticipated future expansion.
Therefore, a device implemented in monolithic silicon would desirably provide a port expansion mechanism. A repeater would also desirably have the additional function of monitoring for a collision among its ports and responding appropriately.
Collision detection and processing complications develop for repeaters because multiple nodes may be coupled to a single port (for example, an AUI port) through a mixing segment, requiring collision detection from the single port.
The second complication develops from a linking segment connecting two repeaters together. Special circuitry must enable two repeaters sending JAM patterns to each other to cease transmission when these active ports are the only ports left jamming each other. Otherwise, the two repeaters would JAM each other forever.
Repeaters perform multiple functions outlined in section 9 of the IEEE 802.3 Standard and the Twisted Pair Transceiver functions of the draft 10-Base-T standard. Integration of a repeater with a MAU simplifies installation of twisted pair networks as well as decreases overall manufacture installation and hardware costs.